Field of Invention
The present invention relates to a method of controlling an electric continuous variable valve timing apparatus, and more particularly, to a method of controlling an electric continuous variable valve timing apparatus, which improves starting performance of an engine.
Description of Related Art
In general, a continuous variable valve timing (CVVT) apparatus refers to an apparatus which adjusts opening and closing timing of a valve of an engine. Particularly, as the CVVT apparatus controls an intake valve in accordance with a driving condition, output of the engine and fuel efficiency may be improved, and exhaust gas may be reduced.
The opening and closing operations of exhaust and intake valves are performed by a rotation of a camshaft.
A general CVVT apparatus is a hydraulic vane type CVVT apparatus. The vane type CVVT apparatus is provided in a small space, and has a merit of being inexpensive.
However, because the vane type CVVT apparatus uses lubricant of the engine as working oil, there is a drawback in that it is difficult to expect fast and accurate response in a state in which pressure of oil is low. Particularly, in a case in which pressure of engine oil is not sufficient, such as in an idle state of the engine, in a high temperature state, in a start state, or the like, a relative phase variation of the camshaft is difficult, and excessive leakage of exhaust gas may occur. In addition, by a shortfall of pressure of oil and excessive viscosity of oil at the time of cold starting, an operation of the hydraulic CVVT apparatus may be impossible. Therefore, starting is performed at a parking position fixed by a lock pin.
An electric CVVT apparatus, which may electrically control valve timing, has been developed to supplement the drawback. However, in the electric CVVT apparatus, at the time of an abnormal operation in which a phase of the camshaft is excessively advanced or retarded, excessive noise may occur due to interference between the camshaft and a stopper of the CVVT apparatus.
In addition, in the electric CVVT apparatus, by strategic use of late intake valve closing, when a closing operation of an intake valve is retarded, an effective compression ratio is lowered, and starting is not easy. Meanwhile, starting may be performed by operating a phase of a cam to a position where starting is possible by the CVVT apparatus during cranking, but a starting retard according to an advance of the camshaft may occur.
As a method of overcoming the aforementioned problem, a phase of the camshaft may be adjusted to a position where next starting is advantageous at the time of starting off.
However, in a phase control of the camshaft by the CVVT apparatus at the time of starting off, when it is required not only to determine whether a moving direction of the camshaft, in which a phase of the crankshaft reaches a target position for starting during cranking, is an advance direction or a retard direction, and but also to move the camshaft from a retard position to an advance position, a starting retard due to a response retard of the CVVT apparatus may occur.
The information disclosed in this Background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.